1. Field of the Application
The present application relates to a method for manufacturing a structural element from composite material having a friction surface, in particular a method for manufacturing by molding a structural element, such as a shroud of an axial turbine engine compressor. The invention also relates to a structural element, such as a shroud of an axial turbine engine compressor.
2. Description of Related Art
EP 0 219 445 discloses an inner shroud of a rectifier grid of a compressor of an axial turbine. The inner shroud is made of composite material and is composed of an inner ring having a laminated structure comprising layers of Kevlar® polyamide fibers embedded in an epoxy resin. The shroud also comprises a series of embossed sections designed to be glued to the inner ring and receive the blade roots. Such sections are also made of composite material consisting of glass fibers embedded in resin. A seal cooperating with two fins of the rotor is added to the interior surface of the inner ring. Together with the two fins, the seal forms a labyrinth seal. The construction of the composite inner shroud of this document is complicated because it requires manufacturing and assembling of the several elements composing it. Moreover, the teaching of this document is limited to an inner shroud.
U.S. Pat. No. 4,135,851 discloses an abradable lining of an outer shroud of a compressor or axial turbine. The lining is ring-shaped, designed to be inserted and then fastened, e.g. by gluing, to the shroud, which is probably metallic. The lining is formed from a ring-shaped support comprising corrugated metal sheets and a layer of abradable material fastened to the interior surface of the support. The support made of corrugated metal sheets allows for compensating certain deformations of the abradable layer, thus avoiding possible damages to the blade tips of the rotor and/or the shroud upon contact between these two elements during operation of the machine. This type of construction is also rather complicated as it implies making several elements and assembling them. Different methods for manufacturing abradable layers on a metal shroud of a turbine engine are known.
For instance, WO 2005/014979 discloses a method allowing for a metallic material as slurry to be applied to a surface by dipping, brushing, spraying, or vapor phase deposition, and for porosity to be controlled during curing. The material applied comprises plastic microbeads. The layer applied becomes porous during curing due to vaporization of the microbeads. However, this method is limited to forming an abradable layer on a metal shroud.
The teachings detailed before fail to offer a simple solution for making a composite structural element, such as a turbine engine shroud, having an abradable surface designed to frictionally engage a moving element. Indeed, the solutions offered by these teachings provide at least the separate application of an abradable layer of a kind which is different from the structural element and by an application method which is different from the manufacturing of the element as such. Moreover, a sand-blasting operation of the surface of the element on which the abradable material is to be applied is often necessary in order to ensure satisfactory adherence.
Although great strides have been made in the area of manufacturing structural elements, many shortcomings remain.